1) Field of the Invention
The present invention relates generally to head height control for an agricultural implement such as a cotton harvester, and, more specifically, to lift system for a high capacity stripper head which is automatically controlled by at least two transversely offset sensing shoes.
2) Related Art
Ultra-narrow row cotton (UNRC) strippers typically include a relatively wide fingerhead having narrowly spaced fingers. A typical fingerhead attachment is shown in U.S. Pat. No. 4,358,921 assigned to Allis-Chalmers. Cotton plants are directed between the fingers which remove the cotton bolls from the plants. Automatic height sensing systems typically are used to maintain the fingerhead close to the ground for efficient operation but far enough above the ground to prevent the fingers from digging into the dirt. Existing fingerhead height sensing systems use a constant flow hydraulic system wherein hydraulic fluid flows continuously through a valve to a hydraulic cylinder and then through a small orifice. The valve is tied to a ground sensing shoe through a mechanical linkage to control flow to and from the cylinder to maintain the fingers slightly above the ground. Such a system has several drawbacks. The constant oil flow through the orifice creates excess heat and wastes power. The orifices have to be sized to the weight of the head and are prone to plugging from contamination. Any change in the weight of the head or the viscosity of the oil changes the response of the head.
For relatively wide heads, at least two height sensing shoes are required, usually one at each end of the head, to assure that the head will lift over the highest ground in uneven conditions. Mechanically tying the two sensing shoes together becomes difficult, and some systems rely on relatively complicated electronic or hydraulic controls to assure proper head height control for wide heads operating on uneven terrain. Systems such as shown in U.S. Pat. No. 4,147,016 assigned to Deere & Company include a pair of independently operated cylinders for twisting the head to adjust the height of each of the ends in accordance with height sensing shoes at those ends. Maintaining fast, predictable response and precise control of a large head has been a continuing problem.